Fast curing polydiorganosiloxanes

ABSTRACT

The present invention concerns α-silyl terminated polydiorganosiloxanes, a method of making the α-silyl terminated polydiorganosiloxanes, and sealant compositions containing said compounds and a method of using such sealant compositions.

FIELD OF THE INVENTION

This invention relates to polydiorganosiloxanes, a method of producingthe same, sealant compositions containing the polydiorganosiloxanes ofthe invention and a method of using such sealant compositions.

BRIEF DESCRIPTION OF THE RELATED ART

In the synthesis of room-temperature-vulcanizing sealants (RTV sealants)based on silicones, so-called silanol terminated polydiorganosiloxanes,are widely used as initial compounds.

Generally, RTV sealants based on silicone are created in two steps.First the silanol terminated polydiorganosiloxanes are reacted with amultifunctional silane, whereby the silanol end group is substantiallydisplaced by the multifunctional silane. In a second step the resultantsilane terminated polyorganosiloxane is exposed to moisture to behydrolyzed and condensed to form cross-linked sealants.

Most commonly used systems rely on the presence of acetoxy, enoxy,oxime, methoxy and amine functionalized silanes for coupling with thesilanol terminated polydiorganosiloxane in the above mentioned firststep. Those systems release acetic acid, acetone, oximes, methanol andamines, respectively, upon hydrolysis in the above mentioned secondstep. Besides the toxic character of some of the released compounds,like methanol, various oximes and amines, some compounds like amines andacetic acid possess an offensive smell.

Acetoxy systems in general rely on tin catalysts. The tin level of thosesystems is at least 50 ppm, typically even up to ten times higher. Sincethe use of organometallic compounds conflicts with recent environmentalefforts, such compounds should essentially be avoided where possible.

Moreover, prior art methoxy γ-silane based RTV systems are to becatalyzed by titanates, tin compounds and/or other organometalliccompounds, which are highly questionable for environmental reasons. Eventaking into account the use of organometallic compounds, using ethoxyγ-silanes instead of methoxy silanes to release ethanol instead ofmethanol during moisture catalyzed hydrolysis is not practicable either.This is because ethoxy γ-silane based RTV systems lack reactivity andare therefore disadvantageous regarding skin-over-time, tack-free-timeand vulcanization rate.

Reactivity of alkoxy silanes is not only limited to methoxy derivativesbut to the trimethoxy derivatives, which is due to the reducedreactivity of the dialkoxy analogues. Therefore prior art alkoxy silanecoupled silicones are obtained by the reaction of silanol terminatedpolydiorganosiloxanes with trimethoxy γ-silanes. Since dialkoxyderivatives are not suitable, only cross-linking between suchalkoxysilane terminated polydiorganosiloxanes can occur and a regulatorymere chain-extension by use of dialkoxy derivatives instead of trialkoxyderivatives is not possible.

U.S. Pat. No. 5,457,148 (Lucas et al.) describes an RTV vulcanizablesilicone rubber composition and process for the manufacture thereofhaving a good application rate and good thixotropy, which comprises apolyalkoxy terminated polydimethylsiloxane and a low viscosity silanolstopped polydimethylsiloxane, whereby the composition containssignificant amounts of an organo tin catalyst, which are to be avoidedin the present invention.

Published international Pat. Appl. No. WO 03/008485 (Schindler et al.)describes compositions usable as joint compounds on silicone basis,eliminating alcohols while cross-linking to elastomers takes place.Those compounds are synthesized from silanol terminatedpolydiorganosiloxanes, isocyanato silanes and silazanes, whereby theemployed silanes are limited to isocyanato silanes due to the couplingmechanism—urea bond formation by reaction with silazanes—to the silanolgroups. The compositions used in the examples contain significantamounts of tin compounds and skin-over-times are 15 min or more.

Accordingly, besides overcoming the drawbacks of the above mentionedprior art sealants, the objects and advantages of the present inventionare:

-   (a) to reduce the use of RTV silicone sealant systems containing or    releasing toxic and/or environmentally questionable compounds;-   (b) to provide RTV silicone sealants possessing fast curing speeds,    thus minimizing curing time and enabling soonest possible use of the    facilities sealed; and-   (c) to provide RTV silicone sealants which are customizable to    comply with different curing conditions, like moisture, curing time    and the like, to provide sealants with adjustable skin-over-times;    tack-free-times and vulcanization rates.

Still further objects and advantages will become apparent from aconsideration of the ensuing description.

SUMMARY OF THE INVENTION

In a first embodiment, the present invention is directed to an α-silylterminated polydiorganosiloxane having the following general formula(I):

wherein

-   the radicals R¹ correspond to a straight-chain or branched aliphatic    radical; a cycloaliphatic radical; an aryl radical; an aralkyl    radical; each radical R¹ containing 1 to 12 carbon atoms; each    radical R¹ optionally containing one or more heteroatoms and    optionally being substituted with halogen; the radicals R¹ being    identical or different within the polydiorganosiloxane;-   the radicals R² and R³, which are identical or different, correspond    to a straight-chain or branched aliphatic radical;-   the radicals R⁴ and R⁵, which are identical or different, correspond    to a straight-chain or branched aliphatic radical; or correspond to    OR² and OR³,    -   wherein R² and R³ are defined as above;-   the radicals X and Y, which are identical or different, correspond    to O, S, N, PR⁸ or NR⁸,    -   wherein R⁸ corresponds to H, R⁹, a radical —(C═O)NH—R⁹,        —(C═O)—R⁹ or —(SO₂)—R⁹,        -   wherein R⁹ corresponds to an aliphatic or cycloaliphatic            radical; an aryl radical; each radical R⁹ containing 1 to 12            carbon atoms; and each radical R⁹ optionally containing one            or more heteroatoms;-   the radicals R⁶ and R⁷, which are identical or different, correspond    to a straight-chain or branched aliphatic radical with 1 to 12    carbon atoms; a cycloaliphatic radical, optionally containing one or    more heteroatoms; an aryl radical, optionally containing one or more    heteroatoms; the ═C═O radical; or    -   —(C═O)R¹⁰, wherein        -   R¹⁰ corresponds to a straight-chain or branched aliphatic            radical with 1 to 12 carbon atoms; an Z-R¹¹ radical, wherein            -   Z corresponds to S, O, PR⁸ or NH and            -   R¹¹ corresponds to a straight-chain or branched                aliphatic radical with 1 to 12 carbon atoms;-   n being from 10 to 10000 or    salts of organic acids, inorganic acids or quaternization products    thereof.

In a second embodiment, the present invention provides a method ofmaking an α-silyl terminated polydiorganosiloxane or mixtures thereof,comprising:

-   (A) a first step of adding one or more α-silanes of general formula    (II):    -   wherein R², R⁴, and R⁶ are defined as above and X=O, S, PR⁸, N,        NH or NR⁸, R⁸ being defined as above;    -   to one or more silanol terminated polydiorganosiloxanes of        general formula (III):    -   wherein R¹ is defined as above,    -   to react both silanol groups; and optionally,    -   if X=NH-   (B) a second step, wherein one or more compounds selected from the    group consisting of R⁹NCO, R⁹(CO)C¹, R⁹COOH, (R⁹CO)₂O, R⁹SO₂Cl and    alkylating agents such as alkyl iodide are added to achieve a    complete or partial reaction between the X radical of the product    obtained in step (A) and the selected compound or compounds.

In an alternative method, if X=the NH radical, a partial or completereaction of the compound according to general formula (II) with one ormore of the compounds listed under step (B) can be carried out prior tothe reaction with the compound according to general formula (III). Insome cases using this alternative method it is desired to add anadditional basic catalyst, like butyl lithium or lithium alkoxides,lithium hydroxide, potassium or sodium compounds (whereas lithium isreplaced with potassium or sodium in the above mentioned compounds) orLewis bases.

In a fourth embodiment, the present invention is directed to a sealantcomposition, comprising the α-silyl terminated polydiorganosiloxane ofthe invention.

A fifth embodiment of the invention is directed to a method of applyingthe sealant composition of the invention, comprising a first step ofapplying the sealant toga substrate to be sealed, a second step ofexposing the sealant to moisture and an optional third step ofactivating a photolatent base contained in the sealant composition byirradiation.

DETAILED DESCRIPTION

In a preferred embodiment of the α-silyl terminated polydiorganosiloxaneof the invention the radicals R¹ correspond to a straight-chain orbranched alkyl radical with 1 to 8 carbon atoms, like methyl, ethyl,n-propyl, iso-propyl, n-butyl, iso-butyl, tert.-butyl and the like. Awidely used alkyl radical in silicones is e.g. methyl. Optionally suchradicals can contain heteroatoms like oxygen, sulfur or nitrogen, suchas an alkoxyalkylene radical, for example. The radicals R¹ canoptionally further contain halogen, like chlorine or fluorine instead ofhydrogen atoms, e.g. in radicals like the perfluoropropylene radical.

Other possible radicals R¹ are aryl radicals, whereby 5-membered and6-membered aryl radicals, like phenyl, are preferred. Optionally thoseresidues may contain heteroatoms, like oxygen, sulfur or nitrogen.Optionally halogen atoms are substituted for hydrogen atoms.

In a further embodiment of the invention the radicals R¹ along the nSi(R¹)₂—O-unit containing polydiorganosiloxane chain can be identical,like e.g. in a polydimethylsiloxane chain; or different, like e.g. in apolytrifluoropropylmethylsiloxane chain, wherein some of the methylgroups of a polydimethylsiloxane chain are substituted by —CH₂—CH₂—CF₃radicals or in a poly(diphenylsiloxane/dimethylsiloxane) copolymerchain, wherein some of the Si(CH₃)₂—O-units are replaced bySi(phenyl)₂—O-units.

In general all radicals R¹ are independent from each other in structureor number along the polydiorganosiloxane chain.

The most common radical R¹ in view of commercial availability of silanolterminated polyorganosiloxanes is methyl.

The radicals R² and R³, which are identical or different, preferablycorrespond to a straight-chain or branched alkyl radical with 1 to 8carbon atoms. In view of the above environmental statements and toxicityreasons the ethyl radical is preferred over the methyl radical.Nevertheless where reactivity of such groups in cross-linking is thecrucial factor, the employment of methyl groups might be considered,since reactivity slows down as the chain length of the alkyl groupincreases.

The radicals R⁴ and R⁵, which are identical or different, preferablycorrespond to a straight-chain or branched alkyl radical with 1 to 8carbon atoms or the OR² and OR³ radicals, wherein R² and R³ have theabove meaning.

In case one or more of R⁴ or R⁵ denote alkyl radicals, cross-linking isreduced compared to the case where one or both of R⁴ and R⁵ correspondto OR² and OR³ radicals. The number of OR² and/or OR³ radicals withinone α-silyl terminated polydiorganosiloxane is determined by theα-silane used as reaction partner with the silanol terminatedpolyorganosiloxane. In case the only α-silanes are trialkoxy α-silanesthe resulting α-silyl terminated polydiorganosiloxane will carry amaximum of 4 OR² and/or OR³ radicals. In case the only α-silanes aredialkoxy α-silanes the resulting α-silyl terminated polydiorganosiloxanewill carry a maximum of 2 OR² and/or OR³ radicals. Nevertheless, if amixture of dialkoxyl α-silanes and trialkoxy α-silanes is employed anynumber of OR² and/or OR³ radicals between 2 and 4 can be adjusteddepending on the ratio between dialkoxyl α-silanes and trialkoxyα-silanes and their reactivity. Generally trialkoxy α-silanes are morereactive compared to dialkoxy α-silanes. Nevertheless their reactivityis also influenced by the XR⁶ or YR⁷ groups, which will be discussedbelow and the nature of the R² and R³ groups which was discussed above.

The radicals X and Y, which are identical or different, correspond to O,S, N or NR⁸, wherein R⁸ corresponds to H, R⁹, a radical —(C═O)NH—R⁹,—(C═O)—R⁹ or —(SO₂)—R⁹, wherein R⁹ preferably corresponds to an alkyl orcycloalkyl radical with 1 to 8 carbon atoms, a 5-membered or a6-membered aryl radical optionally containing heteroatoms. In view of ahigh cross-linking activity, resulting in low skin-over-times andtack-free-times as well as high vulcanization rates, it is preferredthat X and/or Y are NH, which is a radical suitable to auto-catalyze thecross-linking between the α-silyl terminated polydiorganosiloxanes, dueto the basic character of the NH radical.

Moreover, the NH radical-containing α-silanes are also advantageous inview of the reaction with silanol terminated polydiorganosiloxanes,since the basic character of this group typically makes the employmentof catalysts unnecessary.

Further, the α-silyl terminated polydiorganosiloxanes carrying the NHradical as radical X and/or Y can not only be used for sealant purposesas such, but can serve as precursors in a further reaction withisocyanates of the general formula R⁹—NCO, or acid halides of thegeneral formula R⁹—COHal, anhydrides ((R⁹CO)₂O), or R⁹—SO₂Hal, whereinR⁹ corresponds to an aliphatic radical, an aryl radical, each radical R⁹containing 1 to 12 carbon atoms and each radical R⁹ optionallycontaining one or more heteroatoms, whereby R⁹ preferably corresponds toan alkyl radical with 1 to 8 carbon atoms, a 5-membered or a 6-memberedaryl radical optionally containing one or more heteroatoms; and Halcorresponds to an halogen atom, like chlorine.

The α-silyl terminated polydiorganosiloxanes carrying the NH radical asradical X and/or Y can partially or completely be reacted with theisocyanate of the general formula R⁹—NCO, e.g. phenylisocyanate,cyclohexylisocyanate, isopropylisocyanate, or with an acid halide of thegeneral formula R⁹—COHal, e.g. benzoylchloride. This reaction leads tothe products wherein X and/or Y are NR⁸, R⁸ being defined as above. Dueto the complete or partial loss of NH radicals caused by the reactionwith the isocyanate or acid halide, the basic character is partiallylost and reactivity is decreased. This optional reaction is thereforesuitable to customize the α-silyl terminated polydiorganosiloxanes ofthe invention with respect to curing times (skin-over-time,tack-free-time) and vulcanization rates expected by the skilled sealantuser.

Instead of the above mentioned reactions, salts of inorganic acids, likesulfuric acid, hydrochloric acid or organic acids, like benzoic acid,which additionally serves as preservative, terephthalic acid, phthalicacid, caproic acid, fatty acids (like stearic acid), ascorbic acid, ortartaric acid can be formed, to modulate the basic character of theNH-containing silyl radicals as desired.

A further possibility to modulate the basicity of the NH-containingsilyl radicals is to carry out a quaternization reaction of the NHradical, e.g. with a reactive alkyl halide, like methyl iodide.

The radicals R⁶ and R⁷, which can be same or different, preferablycorrespond to a straight-chain or branched alkyl radical with 1 to 8carbon atoms, like methyl, ethyl, n-propyl, iso-propyl, n-butyl,iso-butyl or tert.-butyl radicals; a 5-membered or 6-membered cycloalkylradical, like cyclopentyl or cyclohexyl, which optionally may containone or more heteroatoms, like in the morpholino radical and whichoptionally may contain double bonds a 5-membered or 6-membered arylradical, like the phenyl radical, which optionally may contain one ormore heteroatoms; or the ═C═O radical. The radicals R⁶ and/or R⁷ canalso denote the radical —(C═O)R¹⁰, wherein R¹⁰ corresponds to astraight-chain or branched alkyl radical with 1 to 8 carbon atoms; astraight-chain or branched alkylene radical with 1 to 8 carbon atoms,like the —C(CH₃)═CH₂ radical; a Z-R¹¹ radical, wherein Z corresponds toS, O or NH and R¹¹ corresponds to a straight-chain or branched alkylradical with 1 to 8 carbon atoms, like methyl, ethyl, n-propyl,iso-propyl, n-butyl, iso-butyl or tert.-butyl radicals.

The number of n in general formula (I) typically influences theviscosity of the resultant sealant. The general range for n is 10 to10000. Suitable viscosities of the α-silyl terminatedpolydiorganosiloxanes of the invention can e.g. range from about 1,000to about 900,000 mPa·s (according to Brookfield: Brookfield RVT, 23° C.,Spindle No. 7, 2.5 rpm).

In another embodiment the present invention provides a method of makingα-silyl terminated polydiorganosiloxanes or mixtures thereof, comprising

-   (A) a first step of adding one or more α-silanes of general formula    (II):    -   wherein R², R⁴ and R⁶ are defined as above and X=O, S, PR⁸, N,        NH or NR⁸    -   to one or more silanol terminated polydiorganosiloxanes of        general formula (III):    -   wherein R¹ is defined as above,    -   to react both silanol groups; and optionally    -   if X=NH.-   (B) a second step, wherein a compound selected from the group    consisting of R⁹NCO, R⁹(CO)Cl, R⁹COOH, R⁹SO₂Cl, (R⁹CO)₂O, and    alkylating agents such as alkyl iodide is added to completely or    partially react with the X radical of the product obtained in step    (A).

Suitable α-silanes of formula (II) are e.g.(N-cyclohexylaminomethyl)methyldiethoxysilane,(N-cyclohexylaminomethyl)triethoxysilane(N-phenylaminomethyl)methyldimethoxysilane,(N-phenylaminomethyl)trimethoxysilane,(methacryloxymethyl)methyldimethoxysilane,(methacryloxymethyl)trimethoxysilane,(methacryloxymethyl)methyldiethoxysilane,(methacryloxymethyl)triethoxysilane,(isocyanatomethyl)methyldimethoxysilane,(isocyanatomethyl)trimethoxysilane,N-(morpholinomethyl)trimethoxysilane,N-(morpholinomethyl)triethoxysilan,N-(dimethoxymethylsilylmethyl)-O-methylcarbamate, orN-(trimethoxysilylmethyl)-O-methylcarbamate. Those products are e.g.commercially available from Wacker, Burghausen, Germany under thetradename series GENIOSIL® XL.

Stoichiometrically two α-silanes of formula (II) react with one silanolterminated polydiorganosiloxane, which possesses two —OH end groups.Preferably the α-silanes of formula (II) are added in excess, whereby astoichiometric excess of greater than 1 up to 4 is more preferable and astoichiometric excess of 2 to 3 is most preferable, to ensure completereaction of the silanol groups and to reduce cross-linking reactions.

If step (B) is not carried out, e.g. in case X=O or S; or XR⁶=NCO, acatalyst is preferably added. A suitable catalyst is according to EP564253 butyl lithium.

If step (B) is not carried out because a product wherein X=NH isdesired, the catalyst is preferably omitted, nevertheless the additionof a catalyst does not interfere with the reaction either.

The reactions are usually carried out at temperatures from 0 to 120° C.,preferably 20 to 40° C.

Any of the above α-silyl terminated polydiorganosiloxanes according toformula (I) or mixtures thereof or reaction products obtained by themethods of making, α-silyl terminated polydiorganosiloxanes of theinvention are suitable as sealant components.

Therefore another embodiment of the present invention provides sealantcompositions, comprising one or more α-silyl terminatedpolydiorganosiloxanes according to the invention.

The content of α-silyl terminated polydiorganosiloxanes within thesealant compositions of the invention typically varies between 10 and95% by weight based on the weight of the total composition. Preferablytheir content is in the range of 40 to 80% by weight.

Typically such sealant compositions comprise further additives, likewater scavengers, fillers, plasticizers, adhesion promoters,photosensitizers, pigments and other standard supplementary agents.Since the α-silyl terminated polydiorganosiloxanes of the invention arehighly reactive and moisture sensitive, those additives are preferablymixed with the α-silyl terminated polydiorganosiloxanes of the inventionin a bone-dry (anhydrous) state to prevent interference with storagestability and to prevent premature vulcanization.

Typical water scavengers are e.g. vinyltrimethoxysilane,vinyltripropenoxysilane, carbamatomethylsilanes, tetraethoxysilane,hexamethyldisilanzane, acetoxysilanes, or isocyanates.

Typical fillers in sealant compositions are e.g., silica, carbon black,metal oxides, like titanium dioxide, ferric oxide, aluminum oxide, zincoxide, quartz, calcium carbonate clay, zirconium silicate, gypsum,silicium nitride, boron nitride, barium sulfate, zeolite, glass andplastic powder.

Plasticizers in sealant compositions in general comprise compounds liketrimethylsilyl terminated polydimethylsiloxanes or organic esters ormineralic oils.

Typical adhesion promoters are e.g. 3-aminopropyltriethoxysilane,3-aminopropyltrimethoxysilane, 3-aminopropylmethyldiethoxysilane,3-aminopropylmethyldimethoxysilane, methylaminopropyltrimethoxysilane,1,3,5-tris(trimethylsilylpropyl)isocyanurate,3-glycidoxypropyltrimethoxysilane,3-glycidoxypropylethyldimethoxysilane, 2-glycidoxyethyltrimethoxysilane,2-cyanoethyltrimethoxysilane, 3-cyanopropyltriethoxysilane,isocyanatopropyltriethoxysilane; isocyanatopropyltrimethoxysilane, ormixtures thereof.

Further the α-homologues of the herein before mentioned γ-silanes aresuitable adhesion promoters. Moreover titanium organic compounds, liketetraalkoxytitanates, or organophosphorus compounds are suitableadhesion promoters and known to the one skilled in the art of the fieldof invention.

Other supplementary agents e.g. comprise soluble dyes, inorganic andorganic pigments, anti-oxidants, flame-retardants, UV-stabilziers,biocides, like fungicides, thermal stabilizing agents, rheologicaladditives, and tackifiers.

In case the α-silyl terminated polydiorganosiloxane contained in thesealant composition does not already contain an auto-catalyzing basicnitrogen radical, like NH or other basic radicals, a cross-linkingcatalyst is preferably added to the composition. Upon exposure tomoisture, e.g. ambient humidity, the auto-catalyzing sealant compositionor the sealant composition to which a catalyst was added, will ingeneral start vulcanizing. Nevertheless it is also possible to add oneor more photolatent bases, as e.g. o-nitrobenzyloxicarbonylamine,benzoincarbamate, α,α-dimethylbenzoyloxycarbonylamine,formanilid-derivatives, O-acyloxime, photolatentdiazabicyclo[4.3.0]non-5-ene (PL-DBN) or PL-tertiary amines or amidinesas catalysts and to start vulcanization upon irradiation of suchphotolatent base containing sealants subsequent to their application.Due to irradiation the free base will be created within the sealantcomposition from the photolatent base and vulcanization will start.

Another embodiment of the invention is therefore directed to a method ofapplying the sealant composition of the invention, comprising a firststep of applying the sealant to a substrate to be sealed, a second stepof exposing the sealant to moisture and an optional third step ofactivating a photolatent base contained in the sealant composition byirradiation.

Typical substrates for RTV silicone based sealants comprise e.g. metals,e.g. aluminum, iron, magnesium, copper, chrome, alloys thereof, and thelike, polymers, e.g. polyacrylates, polymethacrylates,polyvinylchlorides, polycarbonates and the like, ceramics, tiles, glass,marble, concrete, granite, sandstone, limestone and wood.

In general it is preferred that the ambient humidity is above 30% ofrelative humidity to ensure a fast curing of the sealants.

In case photolatent bases are used as crosslinking catalysts, anyphotolatent bases possessing suitable basicity are applicable. Besidesthe well-known photolatent bases as described by Cameron et al. in J.Am. Chem. Soc. 118 (1996) 12925, J. Chem. Soc. Perkin Trans. I (1997)2429 and J. Org. Chem. 55 (1990) 5919, by Nishikubo et al. in Polym. J.29 (1997) 450 and Polym. J. 25 (1993) 365, as well as Ito et al. in J.Poly. Sci. Part A: Polym. Chem. 32 (1994) 2177, a new generation ofphotolatent bases has been described by CIBA, Basel, Switzerland (WO03/033500). Prominent species of those photolatent bases are e.g.photolatent diazabicyclononanes, in particular5-benzyl-1,5-diazabicyclo[4.3.0]nonane, wherein the 5-benzyl residuemaybe substituted by one or more substituents. Suitable substituents atthe 5-benzyl residue are halide, like chlorine or bromine, alkylresidues, like methyl, ethyl or propyl, nitril residues, nitro groups,alkoxy groups like methoxy or ethoxy groups or aromatic residues whichare condensed to the residue, as e.g. a 5-(naphth-2-ylmethyl) residue ora 5-(anthracen-9-yl-methyl) residue derived from a 5-(benzyl) residue.It is also possible to introduce a 5-(anthrachinon-2-yl-methyl) residueinstead of the 5-benzyl residue. Besides such substitutions at the5-benzyl residue it is also possible to further substitute thediazacyclononane residue to get photolatent bases like5-benzyl-2-methyl-1,5-diazabicyclo[4.3.0]nonane.

Besides the photolatent diazabicyclononanes it is also possible to usephotolatent diazabicycloundecanes, like for example8-benzyl-1,8-diazabicyclo[5.4.0]undecanes and its derivatives. The8-benzyl residue can be substituted in the same way as shown for the5-benzyl residue in 5-benzyl-1,5-diazabicyclo[4.3.0]nonane. Furthersubstitution at the diazabicyclononane residue is likewise possible.

It is also possible to use photolatent bases comprising two releasablebases within one molecule. An example for such compounds is1,4-bis(1,5-diazabicyclo[4.3.0]nonanylmethyl)benzene. In casephotolatent bases are used in the compositions of the present inventionit is preferable to add photosensitizers to the composition. It isfurther preferable to use one or more substituted or unsubstitutedbenzophenones, thioxanthones, anthrachinones, 3-acylcoumarines or dyeslike oxacines, acridines, phenacines and rodamines as photosensitizers.

Compositions containing photolatent bases require irradiation toliberate or release the free base. The irradiation wavelength used tocause formation of the free base can be varied over a wide range,ranging from the UV region through the visible region into the infraredregion, depending on the photolatent base. Most preferably wave lengthsranging from about 200 to about 700 nm will be used. Suitable radiationcomprises, for example, sunlight or light from artificial light sources.Both point sources and flat radiators are suitable. Examples are carbonarc lamps, xenon arc lamps, medium-pressure, high-pressure andlow-pressure mercury lamps, doped if desired with metal halides (metalhalogen lamps), microwave-stimulated metal vapour lamps, excimer lamps,superactinic fluorescent tubes, fluorescent lamps, incandescent argonlamps, electronic flashlights, xenon flashlights, photographic floodlamps, electron beams and X-rays, produced by means of synchrotrons orlaser plasma. The distance between the lamp and the substrate preferablyrange from about 1 cm to about 2 m, but depends on the light source andthe sensitivity of the photolatent bases as well as the presence orabsence of further photosensitizers.

EXAMPLES PREPARATION EXAMPLES Example 1 Preparation of a Fast CureSilicone RTV Sealant

80 g of silanol terminated polydimethylsiloxane (molecular weight ofapproximately 32,000 g/mol; n—as defined above—is approximately 430) isde-aerated for 10 min at room temperature under vacuum. 0.01 g ofn-butyl lithium (1.6M solution in hexane) is added as catalyst. Theresultant mixture is mixed under N₂ for 2 min (mixer: model PLM 5,obtained from Premier Mill Corp., Reading, Pa., U.S.A.). A mixture of2.03 g of N-(trimethoxysilylmethyl)-O-methylcarbamate and 0.67 g ofN-(cyclohexylaminomethyl)-triethoxysilane is added, and the resultantmixture is mixed under vacuum for 60 min at room temperature. 10.81 g oftrimethylsiloxy terminated polydimethylsiloxane (Dow Corning 200®,Fluid, 1000 CST.) is added as a plasticizer. After mixing for 5 min,6.30 g silica (Aerosil® R 974, obtained from Degussa, Germany) is added.

The resultant mixture is mixed at low blade-speed until the silica iswetted in, and then the mixing continues at a higher blade-speed for 15min to disperse the silica further.

0.18 g hexamethydisilazane is added and the resultant mixture is mixedunder vacuum for 15 min. The resultant mixture is a ready-to-usesealant.

The resultant sealant was tested with respect to its vulcanization rateand skin-over-time at 23° C. and 50% relative humidity. The results areshown in Table 1.

Example 2 Preparation of a Fast Cure Silicone RTV Sealant

85.23 g. of silanol terminated polydimethylsiloxane (molecular weight ofapproximately 32,000 g/mol) is de-aerated for 10 min at room temperatureunder vacuum. A mixture of 1.52 g ofN-(cyclohexylaminomethyl)-methyldiethoxysilan and 1.70 g ofN-(cyclohexylaminomethyl)-triethoxysilane is added under stirring. Theresultant mixture is mixed under vacuum for 60 min at room temperature.Afterwards 7.22 g silica (Aerosil® R 974, obtained from Degussa,Germany) is added in small portions. The mixture is mixed at high speedunder nitrogen atmosphere for 15 min. 0.21 g hexamethydisilazane and1.03 g of γ-aminopropyltriethoxysilane are mixed in. Subsequently 2.06 gof zinc oxide and 1.03 g of titanium dioxide are added. The resultantmixture is stirred under vacuum for 15 min to become a ready-to-usesealant.

The resultant sealant was tested with respect to its vulcanization rateand skin-over-time at 23° C. and 50% relative humidity. The results areshown in Table 1.

Example 3 Preparation of a Fast Cure Silicone RTV Sealant

88.63 g of silanol terminated polydimethylsiloxane (molecular weight ofapproximately 32,000 g/mol) is de-aerated for 10 min. at roomtemperature under vacuum. 0.01 g of n-butyllithium (1.6M solution inhexane) is added as catalyst. The resultant mixture is mixed under N₂for 2 min. A mixture of 0.64 g ofN-(cyclohexylaminomethyl)-methyldiethoxysilan and 2.96 g ofN-(cyclohexylaminomethyl)-triethoxysilane is added, and the resultantmixture is mixed under vacuum for 30 min at room temperature in order tocomplete the end-capping. 0.56 g of phenylisocyanate is added and themixture is mixed for 15 min at room temperature under vacuum. Theprogress of the reaction is controlled by IR spectroscopy. Aftercompletion of the reaction 7.00 g of silica (Aerosil® R 974, obtainedfrom Degussa, Germany) is added whereby the mixture is mixed at lowblade-speed. Afterwards the formulation is mixed with high blade-speedunder nitrogen atmosphere for 15 min in order to disperse the silicahomogenously. 0.20 g hexamethydisilazane is added and the resultantmixture is mixed under vacuum for 15 min. The resultant mixture is aready-to-use sealant.

The resultant sealant was tested with respect to its vulcanization rateand skin-over-time at 23° C. and 50% relative humidity. The results areshown in Table 1.

Comparative Example Commercial Available Sealant

Commercially available ready-to-use, fast curing silicone sealantavailable from Rhodia, Leverkusen, Germany under the tradename “ELCH”sealant. This sealant releases acetic acid while cross-linking occurs.

The sealant was tested with respect to its vulcanization rate andskin-over-time at 23° C. and 50% relative humidity. The results areshown in Table 1. TABLE 1 Comparative Example 1 Example 2 Example 3Example skin-over-time 5 3 7.5 6 [min] vulcanization 0.84 0.83 0.73 0.25rate [mm/2 h] vulcanization 4.8 4.6 4.5 3.7 rate [mm/d]

Examples 4 to 8 Preparation of Silicone RTV Sealants Customized inSkin-Over-Time and Tack-Free-Time

40 g of silanol terminated polydimethylsiloxane (molecular weight ofapproximately 32,000 g/mol) is de-aerated for 10 min at room temperatureunder vacuum and mixed with 1.65 g ofN-(cyclohexylaminomethyl)-triethoxysilane. The resultant mixture ismixed under nitrogen atmosphere for 15 min at room temperature.Afterwards phenylisocyanate (PIC) is added (Example 4: 0.00 g PIC;Example 5: 0.18 g PIC; Example 6: 0.36 g PIC; Example 7: 0.54 g PIC; andExample 8: 0.72 g PIC). The resultant reaction mixture is further mixedunder nitrogen atmosphere at room temperature until no isocyanateabsorption was detectable in an infrared spectrum. The different amountsof PIC added allowed different degrees of conversion of the basicnitrogen atom in the terminal N-cyclohexylaminomethyl radicals to ureagroups. The conversion was 0% for Example 4, 25% for Example 5, 50% forExample 6, 75% for Example 7 and 100% for Example 8 based on the totalsilane content.

The resultant RTV silicone sealant mixtures were tested regarding theirskin-over-time and tack-free-time at 23° C. and 50% relative humidity.The respective results are given in Table 2. TABLE 2 Ex- ample 4 Example5 Example 6 Example 7 Example 8 skin-over-time 3.5 5 10 12 >480 [min]tack-free-time 19 34 73 >480 >1440 [min]

The results shown in Table 2 clearly demonstrate that a conversion ofthe secondary amino group in the terminal N-cyclohexylaminomethylradicals to urea groups significantly decreases the reactivity of thesealants resulting in increased skin-over-times and tack-free-times.Therefore in case a longer processability of the sealants is preferredand high-speed curing is not desired or of priority, the environmentallyadvantageous sealants of the present invention can be customized to theneed of the skilled worker in the field of sealants.

Although the description and examples above contain many specificities,these should not be construed as limiting the scope of the invention butas merely providing illustrations of some of the presently preferredembodiments of this invention. Thus the scope of the invention should bedetermined by the appended claims and their legal equivalents, ratherthan by the examples given.

1. An α-silyl terminated polydiorganosiloxane having the followinggeneral formula (I):

wherein the radicals R¹ are selected from the group consisting ofstraight-chain aliphatic radicals, branched aliphatic radicals,cycloaliphatic radicals, aryl radicals, and aralkyl radicals, eachradical R¹ containing 1 to 12 carbon atoms and optionally one or moreheteroatoms and optionally being substituted with halogen, the radicalsR¹ being identical or different within the polydiorganosiloxane; theradicals R² and R³, which are identical or different, are selected fromthe group consisting of straight-chain aliphatic radicals and branchedaliphatic radicals; the radicals R⁴ and R⁵, which are identical ordifferent, are selected from the group consisting of straight-chainaliphatic radicals, branched aliphatic radicals, OR² and OR³, wherein R²and R³ are defined as above; the radicals X and Y, which are identicalor different, are selected from the group consisting of O, S, N, PR⁸ andNR⁸, wherein R⁸ is selected from the group consisting of H, —(C═O)NH—R⁹,—(C═O)—R⁹ and —(SO₂)—R⁹, wherein R⁹ is selected from the groupconsisting of aliphatic radicals, cycloaliphatic radicals, and arylradicals, each radical R⁹ containing 1 to 12 carbon atoms and optionallycontaining one or more heteroatoms; the radicals R⁶ and R⁷, which areidentical or different, are selected from the group consisting ofstraight-chain aliphatic radicals with 1 to 12 carbon atoms, branchedaliphatic radicals with 1 to 12 carbon atoms, cycloaliphatic radicals,cycloaliphatic radicals containing one or more heteroatoms, arylradicals, aryl radicals containing one or more heteroatoms, ═C═O, and—(C═O)R¹⁰, wherein R¹⁰ is selected from the group consisting ofstraight-chain aliphatic radicals with 1 to 12 carbon atoms, branchedaliphatic radicals with 1 to 12 carbon atoms, and Z-R¹¹, wherein Z isselected from the group consisting of S, O, PR⁸ and NH and R¹¹ isselected from the group consisting of straight-chain aliphatic radicalswith 1 to 12 carbon atoms and branched aliphatic radicals with 1 to 12carbon atoms; n is from 10 to 10000; and salts of organic acids,inorganic acids or quaternization products thereof.
 2. The α-silylterminated polydiorganosiloxane of claim 1, wherein the radicals R¹ areselected from the group consisting of straight-chain alkyl radicals with1 to 8 carbon atoms wherein optionally one or more halogen atoms aresubstituted for hydrogen atoms, branched alkyl radicals with 1 to 8carbon atoms wherein optionally one or more halogen atoms aresubstituted for hydrogen atoms, 5-membered and 6-membered aryl radicalsoptionally containing one or more heteroatoms and wherein optionally oneor more halogen atoms are substituted for hydrogen atoms, the radicalsR¹ being identical or different within the polydiorganosiloxane.
 3. Theα-silyl terminated polydiorganosiloxane of claim 1, wherein the radicalsR² and R³, which are identical or different, are selected from the groupconsisting of straight-chain and branched alkyl radicals with 1 to 8carbon atoms.
 4. The α-silyl terminated polydiorganosiloxane of claim 1,wherein the radicals R⁴ and R⁵, which are identical or different, areselected from the group consisting of straight-chain and branched alkylradicals with 1 to 8 carbon atoms, OR² and OR³, wherein R² and R³ areidentical or different and are selected from the group consisting ofstraight-chain and branched alkyl radicals with 1 to 8 carbon atoms. 5.The α-silyl terminated polydiorganosiloxane of claim 1, wherein theradicals X and Y, which are identical or different, are selected fromthe group consisting of O, S, N, PR⁸ and NR⁸, wherein R⁸ is selectedfrom the group consisting of H, —(C═O)NH—R⁹, —(C═O)—R⁹ and —(SO₂)—R⁹,wherein R⁹ is selected from the group consisting of alkyl and cycloalkylradicals with 1 to 8 carbon atoms and 5-membered or and 6-membered arylradicals optionally containing one or more heteroatoms.
 6. The α-silylterminated polydiorganosiloxane of claim 1, wherein the radicals R⁶ andR⁷, which are the same or different, are selected from the groupconsisting of straight-chain and branched alkyl radicals with 1 to 8carbon atoms, 5-membered and 6-membered cycloalkyl radicals, optionallycontaining one or more heteroatoms and optionally containing one or moredouble bonds, 5-membered and 6-membered aryl radicals, optionallycontaining one or more heteroatoms, ═C═O, and —(C═O)R¹⁰, wherein R¹⁰ isselected from the group consisting of straight-chain and branched alkylradicals with 1 to 8 carbon atoms, straight-chain and branched alkyleneradicals with 1 to 8 carbon atoms, Z-R¹¹ radicals, wherein Z is selectedfrom the group consisting of S, O, PR⁸ and NH and R¹¹ is selected fromthe group consisting of straight-chain and branched alkyl radicals with1 to 8 carbon atoms.
 7. The α-silyl terminated polydiorganosiloxane ofclaim 1, wherein n is between 10 and 10000 and selected to provide theα-silyl terminated polydiorganosiloxane with a viscosity of 1,000 to900,000 mPa·s (according to Brookfield: Brookfield RVT, 23° C., SpindleNo. 7, 2.5 rpm).
 8. The α-silyl terminated polydiorganosiloxane of claim1, wherein the radical X is NH and wherein said NH radical is furtherreacted with one or more CL quaternization reagents selected from thegroup consisting of alkyl halides or wherein said NH radical is furtherreacted with one or more inorganic acids or organic acids selected fromthe group consisting of sulfuric acid, hydrochloric acid, benzoic acid,terephthalic acid, phthalic acid, caproic acid, stearic acid, ascorbicacid and tartaric acid.
 9. A method for making an α-silyl terminatedpolydiorganosiloxane, the method (I) comprising: (A) a first step ofadding one or more α-silanes of general formula (II):

wherein R² is selected from the group consisting of straight-chain andbranched aliphatic radicals; R⁴ is selected from the group consisting ofstraight-chain or branched aliphatic radicals, OR² and OR⁸, X isselected from the group consisting of O, S, PR⁸, NR⁸ and N, wherein R⁸is selected from the group consisting of H, —(C═O)NH—R⁹, —(C═O)—R⁹ and—(SO₂)—R⁹; wherein R⁹ is selected from the group consisting of aliphaticand cycloaliphatic radicals and aryl radicals, each radical R⁹containing 1 to 12 carbon atoms and each radical R⁹ optionallycontaining one or more heteroatoms; and R⁶ is selected from the groupconsisting of straight-chain and branched aliphatic radicals with 1 to12 carbon atoms, cycloaliphatic radicals, optionally containing one ormore heteroatoms, aryl radicals, optionally containing one or moreheteroatoms, ═C═O, and —(C═O)R¹⁰, wherein R¹⁰ is selected from the groupconsisting of straight-chain and branched aliphatic radicals with 1 to12 carbon atoms and Z-R¹¹ radicals, wherein Z is selected from the groupconsisting of S, O, PR⁸ and NH and R¹¹ is selected from the groupconsisting of straight-chain and branched aliphatic radicals with 1 to12 carbon atoms; to one or more silanol terminated polydiorganosiloxanesof general formula (III):

wherein R¹ is selected from the group consisting of straight-chain andbranched aliphatic radicals, cycloaliphatic radicals, aryl radicals, andaralkyl radicals, each radical R¹ containing 1 to 12 carbon atoms andoptionally containing one or more heteroatoms and optionally beingsubstituted with halogen, the radicals R¹ being identical or differentwithin the polydiorganosiloxane; to react both silanol groups; andoptionally, if X=NH (B) a second step, wherein one or more compoundsselected from the group consisting of R⁹NCO, R⁹(CO)Cl, R⁹COOH, R⁹SO₂Cl,(R⁹CO)₂O and alkylating agents, wherein R⁹ is selected from the groupconsisting of aliphatic radicals and aryl radicals, each radical R⁹containing 1 to 12 carbon atoms and optionally containing one or moreheteroatoms; are added to achieve a complete or partial reaction betweenthe X radical of the product obtained in step (A) and the selectedcompound or compounds.
 10. The method according to claim 9, wherein step(A) is carried out in the presence of a catalyst selected from the groupconsisting of butyl lithium, lithium alkoxides, lithium hydroxide, butylpotassium, potassium alkoxides, potassium hydroxide, butyl sodium,sodium alkoxides, sodium hydroxides and Lewis bases.
 11. The method ofclaim 9, wherein the α-silane according to formula (II) is selected fromthe group consisting of (N-cyclohexylaminomethyl)methyl-diethoxysilane,(N-cyclohexylaminomethyl)triethoxysilane,(N-phenylaminomethyl)methyldimethoxysilane,(N-phenylaminomethyl)trimethoxysilane,(methacryloxymethyl)methyldimethoxysilane,(methacryloxymethyl)trimethoxysilane,(methacryloxymethyl)methyldiethoxysilane,(methacryloxymethyl)triethoxysilane,(isocyanatomethyl)methyldimethoxysilane,(isocyanatomethyl)trimethoxysilane, andN-(trimethoxysilylmethyl)-O-methylcarbamate.
 12. A sealant compositioncomprising an α-silyl terminated polydiorganosiloxane according toclaim
 1. 13. The sealant composition according to claim 12, furthercomprising one or more compounds selected from the group consisting ofwater scavengers, fillers plasticizers, adhesion promoters,photosensitizers and pigments.
 14. The sealant composition according toclaim 12, wherein the α-silyl terminated polydiorganosiloxane comprisesabout 10% by weight to about 95% by weight of the sealant composition.15. The sealant composition according to claim 12, further comprising across-linking catalyst selected from the group consisting of Lewisbases, amines, amidines, and photolatent bases.
 16. The sealantcomposition according to claim 15 wherein the cross-linking catalyst isa photolatent base, the photolatent base being selected from the groupconsisting of 5-benzyl-1,5-diazabicyclo[4.3.0]nonane and8-benzyl-1,8-diazabicyclo[5.4.0.]undecane, wherein the benzyl residue ineach can further be substituted by halide, alkyl, nitril, nitro, alkoxyor aromatic residues condensed to the benzyl residue.
 17. A method ofusing the sealant composition of claim 12, comprising a first step ofapplying the sealant composition to a substrate to be sealed; a secondstep of exposing the sealant composition to moisture; and an optionalthird step of activating a photolatent base contained in the sealantcomposition by irradiation.